If *estimatable existed, it would mean it is possible to estimate this, not it should be possible.. The difference is important only in technical contexts, of which I would guess AGILE is one.
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TimLymingtonJan 17 '14 at 12:13

3 Answers
3

Why is estimatable not a real English word? The -able suffix is productive, and dictionaries very often do not include words which can be deduced from their constituent parts, particularly since they can only include words in reasonably common usage. There is a trade-off: if they do not include words which can be broken down easily and their component parts looked up, there is more space for slightly less common words which can't be deduced as easily.

+1! I remember once hearing an Italian exchange student tell a Venezuelan (about learning English/vocabulary), "... and if you still can't figure out the right word, make one up. They do it all the time!" Just because we "make up" a word, doesn't mean it's meaningless! Language is about communication, and if a construct is able to clearly convey meaning, there's nothing wrong with it.
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Brian SJan 17 '14 at 16:39

@BrianS Up to a point. Issual, for example, is not to be preferred to issue; or expiration to expiry. -able can be added to more-or-less anything, but even there there are special forms like calculable rather than calculatable.
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Andrew Leach♦Jan 17 '14 at 17:13

Estimable certainly is a real English word, and, as any good dictionary will tell you, it means 'worthy of great respect'. It doesn't mean is 'capable of being estimated'. I know of no single word that means that.

Yes, indeed. I'll blame dyslexia for that one... Silly me. Of course estimable is fine but indeed does not mean 'capable of being estimated'!
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SardathrionJan 17 '14 at 12:14

There are dictionaries on the surface web( and not the deep web )which states otherwise(estimable has multiple meaning :worthy of respect and able to be estimated),but I feel (intuition and not innuendo)there must be a better word for being estimable(which a stats person might now @cross validated)-:(using " surface web" is an innuendo(insinuation)that this question could have been easily referred on the net)
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ArgotJan 17 '14 at 13:39

As Andrew Leach says in his answer, it is not not a real word; in fact, Google Scholar shows 1880 results of the word "estimatable".

While not a large enough number of uses to make it standard usage, a quick scroll shows that most of the publications are in mathematics and statistics (and, of course, here the results are limited to scholarly articles). The sciences often "create" words, and these words can well become standard usage within a particular field. A similar example would be "rounding", as in "going on rounds", commonly used in nursing but not in standard dictionaries with that definition.

My search for "estimatable" in normal Google mostly brings up either the same sort of usage or questions about its usage (such as this).

As such, I would say it is safe to use in the particular context in which it does currently get used, but not formally elsewhere.

Unfortunately, I don't have any good alternatives off the top of my head.